previousIndex 使用 Angular Material 拖放 + cdk 虚拟滚动意外跳转答案

【问题标题】：previousIndex unexpectedly jumps with Angular Material drag/drop + cdk virtual scrollingpreviousIndex 使用 Angular Material 拖放 + cdk 虚拟滚动意外跳转
【发布时间】：2022-02-16 16:54:09
【问题描述】：

将 Angular 与 Angular Material 结合使用，我创建了一个具有拖放列表的示例应用程序，其中一个使用虚拟滚动。但是，对于某些项目，drop 事件的previousIndex 值会突然跳转到不同的值。我很困惑。

复制步骤

将数字 1 到 10 从“待办事项”列表拖到“完成”列表中。当包含“10”的卡片被丢弃时，会转移错误的卡片，并且启用该操作的previousIndex 会从控制台日志中看到的从 0 跳转到 1。

代码

Stackblitz 是 here。

HTML


<div class="whole_thing" cdkDropListGroup>

  <div class="example-container">
    <h2>To do (CDK virtual scroll)</h2>

    <div
      cdkDropList
      [cdkDropListData]="todo"
      class="example-list"
      (cdkDropListDropped)="drop($event)">
      <cdk-virtual-scroll-viewport itemSize="62" class="example-viewport">
        <div class="example-box" *cdkVirtualFor="let item of todo" cdkDrag>{{item}}</div>
      </cdk-virtual-scroll-viewport>
    </div>
  </div>

  <div class="example-container">
    <h2>Done (regular list)</h2>

    <div
      cdkDropList
      [cdkDropListData]="done"
      class="example-list"
      (cdkDropListDropped)="drop($event)">
      <div class="example-box" *ngFor="let item of done" cdkDrag>{{item}}</div>
    </div>
  </div>

打字稿

import { Component, OnInit } from '@angular/core';
import {CdkDragDrop, moveItemInArray, transferArrayItem} from '@angular/cdk/drag-drop';

@Component({
  selector: 'app-thing',
  templateUrl: './thing.component.html',
  styleUrls: ['./thing.component.css']
})
export class ThingComponent implements OnInit {


  constructor() { }

  ngOnInit(): void {
  }

  todo = [
    '1',
    '2',
    '3',
    '4',
    '5',
    '6',
    '7',
    '8',
    '9',
    '10',
    '11',
    '12',
    '13',
    '14',
    '15',
    '16'
  ];

  done = [
    'Get up',
    'Brush teeth',
    'Take a shower',
    'Check e-mail',
    'Walk dog'
  ];

  drop(event: CdkDragDrop<string[]>) {
    if (event.previousContainer === event.container) {
      moveItemInArray(event.container.data, event.previousIndex, event.currentIndex);
    } else {
      transferArrayItem(event.previousContainer.data,
                        event.container.data,
                        event.previousIndex,
                        event.currentIndex);
    }
    //spread operator forces reload
    this.todo = [...this.todo]
    this.done = [...this.done]
    console.log(this.done)
    console.log(event)
  }

}

CSS

.example-container {
  width: 400px;
  max-width: 100%;
  margin: 0 25px 25px 0;
  display: inline-block;
  vertical-align: top;
}

.example-list {
  border: solid 1px #ccc;
  min-height: 60px;
  background: white;
  border-radius: 4px;
  overflow: hidden;
  display: block;
}

.example-box {
  height: 61px;
  /* padding: 20px 10px; */
  border-bottom: solid 1px rgb(192, 11, 11);
  color: rgba(0, 0, 0, 0.87);
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: space-between;
  box-sizing: border-box;
  cursor: move;
  background: white;
  font-size: 14px;
}

.cdk-drag-preview {
  box-sizing: border-box;
  border-radius: 4px;
  box-shadow: 0 5px 5px -3px rgba(0, 0, 0, 0.2),
              0 8px 10px 1px rgba(0, 0, 0, 0.14),
              0 3px 14px 2px rgba(0, 0, 0, 0.12);
}

.cdk-drag-placeholder {
  opacity: 0;
}

.cdk-drag-animating {
  transition: transform 250ms cubic-bezier(0, 0, 0.2, 1);
}

.example-box:last-child {
  border: none;
}

.example-list.cdk-drop-list-dragging .example-box:not(.cdk-drag-placeholder) {
  transition: transform 250ms cubic-bezier(0, 0, 0.2, 1);
}

.example-viewport {
  height: 244px;
  width: 400px;
}

.example-item {
  height: 50px;
}

.whole_thing {
  width: 3000px;
}

.bigscroller {
  height: 600px;
  width: 100%;
}

【问题讨论】：

我认为<cdk-virtual-scroll-viewport 有一些奇怪的地方，因为当我拖放“10”时，它会添加一些其他元素。尝试使用更简单的替代方法

标签： angular angular-material

【解决方案1】：

问题是您使用的是cdk-virtual-scroll-viewport，它用于呈现巨大的列表。为此，列表会被分割，并且只呈现部分内容，这就是为什么你的 indeces 被搞砸了。

我想到的一个解决方法（不确定它是否是最好的）是将cdkVirtualFor 给出的索引作为拖动数据传递并使用它来处理订单。

<cdk-virtual-scroll-viewport itemSize="62" class="example-viewport">
  <div class="example-box" *cdkVirtualFor="let item of todo; let i = index;" cdkDrag [cdkDragData]="i">{{item}}</div>
</cdk-virtual-scroll-viewport>

在组件中

transferArrayItem(event.previousContainer.data,
                        event.container.data,
                        event.item.data,
                        event.currentIndex);

【讨论】：

【解决方案2】：

<cdk-virtual-scroll-viewport
formArrayName="items"
cdkDropList
[itemSize]="options.itemSize"
[perfectScrollbar]="config"
[cdkDropListDisabled]="!options.dragDrop"
(cdkDropListDropped)="onDragDrop($event)"
class="ps"
>
  <div
    *cdkVirtualFor="let item of itemsFiltered$ | async; let currentIndex = index"
    cdkDrag
    cdkDragLockAxis="y"
    [cdkDragData]="currentIndex"
    fxLayout="row"
    class="row"
    [class.drag]="options.dragDrop"
  >
...

onDragDrop(event: CdkDragDrop<AbstractControl[]>) {
    // Fix drag & drop indices inside virtual scroll
    const previousIndex = event.item.data;
    const adjustment = event.previousIndex - previousIndex;
    moveItemInArray(this.items.controls, previousIndex, event.currentIndex - adjustment);
    this.reindex();
    this.emitChanges();
  }

【讨论】：